The concrete industry for the past 35-40 years has not had very many improvements in the way they make cinder blocks. Some of the more prominent manufacturers of block forming equipment have been breaking ground in automation for the past several years but have not developed a calibration device for checking whether the cinder blocks are within tolerance; that is, 75/8.+-.1/8". A currently used system has the blocks being manufactured at a variable rate of up to eight blocks every six seconds. Occasionally a worker will apply a metal template measuring 75/8" to check for height tolerance. This calibration inspection can be done when a cinder block is wet because there is very little shrinkage to consider. The equipment generally used for making cinder block can provide six different configurations, i.e., two 12-inch blocks, two 10-inch blocks, three 8-inch blocks, four 6-inch blocks, six 4-inch blocks, and eight 3-inch blocks, on each pallet.
Previous designs for mechanical solutions to the problems of assuring manufacture of blocks within tolerance did not overcome such obstacles as high Db noise levels, dirty environment, vibration, a fluctuating change in relative humidity, temperature, and wind gusts in the manufacturing environment. Some of these obstacles could not be solved with a standard engineering design. One attempt to solve the problems involved included a calibration device which mounted horizontally and attempted to overcome the difficulty in compensating for the calibration device for material buildup on the 22 by 26 inch steel plate. Over a period of a year, material build-up on the steel plate or pallet does affect the tolerances.
Avoiding preconceived ideas held by those working in the field, a method for solving this problem was discovered that the engineers had overlooked because of the built-in paradigms. A working model was developed and a prototype test was performed in October 1988 at a TARMAC Lone Star block manufacturing site. This test revealed that the device should be able to overcome the variable speed of the conveyor system, and should be shielded in case of an accident (e.g., kickback). The prototype calibration device proved very successful in this test. The particular device tested interfaced with a programmable logic controller, proximity sensor, and a marking device that would score the cinder blocks that were out of tolerance.
The plant where the alpha test was run produces 12 million blocks a year with about 3 percent in defects. The manufacturer loses money when he has to sell a cinder block as a second. As an example of the potential cost of cumulative errors in cinder block tolerance, one plant provided all the cinder blocks for the exterior and interior walls for a school built. Because the cinder blocks were 1/8 inch out of tolerance, after eight tiers the wall was an inch out of line. The architect on the school site caught the mistake and required the replacement of 55,000 cinder blocks. This resulted in the entire section having to be torn down and rebuilt with new block. The cost was many thousands of dollars, and damage to the block manufacturer's reputation.
Additional capabilities that can be included in this calibration device include a counter that tells how many blocks are manufactured, and how many defects are found, having the device inform the worker that the block machine is out of tolerance and by how much, and for the device to shut off the block machine when it was producing cinder blocks out of tolerance.
In the plant environment tested, the production rate ranged from a slow 900 blocks to a fast 1500 blocks per hour per machine. The average speed at the block plant was approximately 1200 blocks per hour with two machines running concurrently.
In one embodiment of the present invention, if the sensing device measures a set of blocks that is out of tolerance, an audible alarm sounds and an LED display shows whether the tolerance was high or low and by how much, and at the same time the block is marked with a raking action. This concept was rejected for a preferred embodiment because marking a bad block only adds to the problem, and it makes better business sense to correct the problem immediately rather than incur the costs involved with manufacturing a bad block.
Accordingly, one object of the invention is to provide a calibration device and system that provides a combination of the following capabilities: Performing measurement tolerance to 0.015 inch, continuous self-calibration, simplified operational control, pallet tolerance, a supervisory control panel, data history, a visual and/or audio alarm, ruggedized construction, and multiple configuration measurement.
Another object of the invention is to provide the dual advantage of first, saving money for the customer by preventing the manufacturing of bad blocks, and second, improving the quality of the manufactured block worldwide.
Another object of the invention is to provide a system that can be installed quickly, with modular components, that provides low maintenance, that is very user friendly, and that can be utilized as part of new equipment or as a field add-on to existing units.
One of the features that has been designed into this product to overcome such obstacles as high Db noise levels, dirty environment, vibration, and a fluctuating change in relative humidity, temperature, and wind gusts, is a self-calibrating ultrasonic sensor.
An embodiment of the invention uses independently measuring ultrasonic sensors mounted vertically over a conveyor system. The sensors are adjustably placed so as to span the entire number of cinder blocks across the pallet on the conveyor system. The sensors take measurements of the heights of the cinder blocks and compare them to preset specification criteria. At the same time, the number of good and bad pallets manufactured is counted.
One embodiment of a system according to the present invention provides multiple measurements (100 measurements every 3 seconds) with each transducer, then computes an average and compares it to the plant's tolerance specification. All out-of-tolerance pallets are rejected. If three consecutive pallets are detected with height calculations that are out of tolerance, an alarm will sound, a strobe light will light and revolve, or a beeper will be activated, so that the block manufacturing machine can be adjusted. Alternatively, a signal may be sent to the pallet dumper when an out-of-tolerance pallet is detected, so that the blocks of that pallet may be destroyed and recycled for new block construction.
One embodiment of apparatus for operating the method of the invention comprises three elements--a bracket, which houses a controller circuit card operating a control and measurement algorithm of the method of the invention, signal generators, and transducers; a computer for providing overall control of the process, and a power panel with an attached strobe light. This apparatus can operate with different settings, and information on multiple configurations can be placed into and stored in memory.
The computer and accompanying software include WINDOWS capability and comprise a WINDOWS based monitor application that affords a graphical representation of what is calibrated and observed. If an alarm sounds, the monitor will show how much out tolerance and whether the equipment needs to be to be raised or lowered. Additionally, a 3 Dimensional model illustrates whether the out-of-specification tolerance was on the left, right or in the center. A control panel in a WINDOWS application running on a computer gives either a 3-Dimensional graphical representation, or actual measurement data detailing the out-of-tolerance condition so it can be corrected quickly.
An authorized user (a password can be set so that only a foreman or other authorized person can perform this function), can activate the tolerance setting and use either keyboard or mouse for setting display characteristics (e.g., whether to measure the distance from the transducers of all the ultrasonic sensors to the pallet in inches or in centimeters) or, if necessary, to activate the calibration routine which can automatically perform its own distance calibration. The user can also set the height that is required for the block, what tolerances are allowed, what type of alarm should be given, etc.
As an additional feature, the invention includes self-diagnostics, to pinpoint malfunctioning equipment in case of a transducer failure.
The control panel is ruggedized, so that it can be washed off with water with no ill effects. The strobe light is designed to be seen from far distances in fairly well-lit environments.